With the exception of alum, emulsion-based vaccine adjuvants have been administered to far more people than any other adjuvant, especially since the 2009 H1N1 influenza pandemic. The number of clinical safety and immunogenicity evaluations of vaccines containing emulsion adjuvants has correspondingly mushroomed. In this review, the authors introduce emulsion adjuvant composition and history before detailing the most recent findings from clinical and postmarketing data regarding the effects of emulsion adjuvants on vaccine immunogenicity and safety, with emphasis on the most widely distributed emulsion adjuvants, MF59® and AS03. The authors also present a summary of other emulsion adjuvants in clinical development and indicate promising avenues for future emulsion-based adjuvant development. Overall, emulsion adjuvants have demonstrated potent adjuvant activity across a number of disease indications along with acceptable safety profiles.